Flip-chip semiconductor package structure and process for fabricating the same

ABSTRACT

An advanced flip-chip packaging technology is proposed, which is characterized in the forming of a metal dam over the substrate to serve three different utilization purposes. First, the metal dam can help provide a specific fillet width to the underfilled material under the flip chip so as to allow the joint between the flip chip and the substrate to have increased robustness against thermal stress. Second, the metal dam can serve as a mechanical reinforcement to the substrate to prevent package warpage. Third, the metal dam can additionally serve as a heat-dissipation structure to help the heat dissipation from the flip chip. These benefits allow the finished package product to be highly assured in quality and reliability.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to semiconductor packaging technology, andmore particularly, to a flip-chip semiconductor packaging technologythat can be used for the fabrication of a flip-chip package structurehaving increased structural robustness to prevent package warpage aswell as having increased heat-dissipation efficiency.

[0003] 2. Description of Related Art

[0004] The flip-chip packaging technology is an advanced semiconductorpackaging technology which differs from conventional technologyparticularly in that the chip is mounted in an upside-down manner overthe substrate and electrically coupled to the same by means of theball-grid array (BGA) technology After the flip chip is readily bondedin position, however, a gap would be undesirably left between the chipand its underlying surface, which, if not underfilled, would easilycause the flip chip to suffer from fatigue cracking and electricalfailure due to thermal stress when the entire package structure is beingsubjected to high-temperature conditions. As a solution to this problem,it is an essential step in flip-chip package fabrication to fill anunderfill material, such as resin, into such a gap. The underfilledresin, when hardened, can serve as a mechanical reinforcement for theflip chip to cope against thermal stress. The involved fabricationprocess is customarily referred to as flip-chip underfill. Aconventional flip-chip package fabrication process is briefly depictedin the following with reference to FIGS. 1A-1B.

[0005] Referring to FIG. 1A, by the conventional process, the first stepis to prepare a substrate 10, which is typically made of an organicmaterial. Next, a semiconductor chip 20 is mounted in a flip-chip mannerover the substrate 10, and which is mechanically bonded and electricallycoupled to the substrate 10 by means of a plurality of solder balls 30.Due to the existence of these solder balls 30, however, a gap 20 a isundesirably left under the flip chip 20. This gap 20 a, if notunderfilled, would easily cause the flip chip 20 to suffer from fatiguecracking and electrical failure due to thermal stress when the entirepackage structure is being subjected to high-temperature conditionsduring subsequent fabrication steps.

[0006] Referring further to FIG. 1B, as a solution to the foregoingproblem, a dispensing needle 40 is used to dispense an underfillmaterial, such as resin 41, onto the substrate area beside the gap 20 a.The dispensed resin 41 will then fill into the gap 20 a throughcapillary action. After the underfill process is finished, however, theundefiled resin 41 would have a fillet part 41 a spread beyond the gap20 a. The width of this underfill fillet part 41 a is roughlyproportional to the height of the gap 20 a under the chip 20 and theamount of the dispensed resin 41, as depicted in the following withreference to FIGS. 2A-2B.

[0007]FIG. 2A shows the case of the chip 20 having a gap height of H₁and an underfill fillet width of W₁, while FIG. 2B shows the case of thechip 20 having a gap height of H₂ and an underfill fillet width of W₂;if H₁<H₂, then W₁<W₂. This means that the conventional flip-chip packagefabrication process, when utilized with various package sizes, wouldresult in different underfill fillet widths. During the fabricationprocess, if the underfill fillet width is overly small or overly large,it would all make the flip chip 20 and the substrate 10 easily subjectedto warpage due to thermal stress and would thus degrade the quality andreliability of the finished package product.

[0008] In view of the foregoing drawback, there exists a need for a newflip-chip package fabrication process that can help the fillet part ofthe underfilled resin to be fixed to a specific width irrespective ofthe height of the flip chip's underneath gap.

[0009] Beside the fillet-width problem, conventional flip-chip packagestructures would suffer from package warpage due to the substrate beingmade of organic material which is typically flexible. A solution to thisproblem is disclosed in the U.S. Pat. No. 6,020,221 entitled “PROCESSFOR MANUFACTURING A SEMICONDUCTOR DEVICE HAVING A STIFFENER MEMBER”.This patent discloses the use of a stiffener member attached to thesubstrate, which not only can serve as a mechanical reinforcement forthe substrate to prevent package warpage, but also can serve as aheat-dissipation means to dissipate the chip-produced heat during activeoperation. This patent, however, is not useful to provide a specificunderfill fillet width, and would be therefore still easily subjected topackage warpage when the underfill fillet width is made overly small oroverly large.

SUMMARY OF THE INVENTION

[0010] It is therefore an objective of this invention to provide a newflip-chip packaging technology, which allows the underfilled resinunderneath the flip chip to have a predetermined fixed underfill filletwidth.

[0011] It is another objective of this invention to provide a newflip-chip packaging technology, which can provide additional mechanicalreinforcement to the substrate so as to allow the package structure tobe more robust to prevent package warpage.

[0012] It is still another objective of this invention to provide a newflip-chip packaging technology, which allow the flip-chip packagestructure to have increased heat-dissipation efficiency.

[0013] In accordance with the foregoing and other objectives, theinvention proposes a new flip-chip packaging technology.

[0014] The flip-chip packaging technology of the invention provides anew package structure which, broadly defined, comprises the followingconstituent parts: (a) a substrate, (b) a semiconductor chip mountedover the substrate through flip-chip technology, with a gap existingbetween the semiconductor chip and the substrate; (c) a metal dam formedaround the semiconductor chip over the substrate, the metal dam beingdimensioned to a predetermined thickness and separated from thesemiconductor chip by a fillet area of a predetermined width; and (d) anunderfill layer formed in the gap under the semiconductor chip, theunderfill layer having a fillet part lying over the fillet area.

[0015] Moreover, the flip-chip packaging technology of the inventionprovides a new package fabrication process which comprises the followingprocedural steps: (1) preparing a substrate having a center areapredefined as a die-bonding area; (2) forming a metal dam around thedie-bonding area over the substrate, the metal dam being dimensioned toa predetermined thickness and separated from the die-bonding area by afillet area of a predetermined fillet width; (3) mounting asemiconductor chip onto the die-bonding area over the substrate throughflip-chip technology, and in which process a gap is undesirably leftbetween the semiconductor chip and the substrate; and (4) dispensing anunderfill material onto the fillet area; the dispensed underfillmaterial subsequently filling into the gap between the semiconductorchip and the substrate through capillary action, thereby forming anunderfill layer having a fillet part over the fillet area, with thewidth of the fillet part being substantially equal to the predeterminedwidth of the fillet area.

[0016] It is a characteristic feature of the invention that the metaldam alone can serve three different utilization purposes. First, themetal dam can help provide a specific fillet width to the underfilllayer under the flip chip so as to allow the joint between the flip chipand the substrate to have increased robustness against thermal stress.Second, the metal dam can serve as a mechanical reinforcement to thesubstrate to prevent package warpage. Third, the metal dam canadditionally serve as a heat-dissipation structure to help heatdissipation from the flip chip. These benefits allow the finishedpackage product to be highly assured in quality and reliability.

BRIEF DESCRIPTION OF DRAWINGS

[0017] The invention can be more fully understood by reading thefollowing detailed description of the preferred embodiments, withreference made to the accompanying drawings, wherein:

[0018] FIGS. 1A-1B (PRIOR ART) are schematic sectional diagrams used todepict a conventional process for fabricating a flip-chip package;

[0019] FIGS. 2A-2B (PRIOR ART) are schematic sectional diagrams used todepict the problem of an inconsistent underfill fillet width whenutilizing the conventional flip-chip packaging technology;

[0020] FIGS. 3A-3D are schematic sectional diagrams used to depict thepackage structure and fabrication steps according to the flip-chippackaging technology of the invention; and

[0021]FIG. 4 is a schematic top view of the package structure shown inFIG. 3A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0022] A preferred embodiment of the flip-chip packaging technology ofthe invention is disclosed in full details in the following withreference to FIGS. 3A-3D and FIG. 4.

[0023] Referring to FIG. 3A together with FIG. 4, by the flip-chippackage fabrication process of the invention, the first step is toprepare a substrate 110, such as an organic substrate. The substrate 110has a center area predefined as a die-bonding area DBA Subsequently, ametal dam 111 is formed around the die-bonding area DBA over thesubstrate 110 to a predetermined thickness T, preferably from 5 μm to 70μm (micrometer), and separated from the boundary of the die-bonding areaDBA by a predetermined fillet width W, preferably from 0.5 mm to 2.5 mm(millimeter). The blank area between the metal dam 111 and the flip chip120 is referred to a fillet area 110 a.

[0024] Referring further to FIG. 3B, in the next step, a semiconductorchip 120 is mounted in a flipped manner directly on the die-bonding areaDBA over the substrate 110 and which is electrically coupled to thesubstrate 110 by means of a plurality of solder balls 130. Due to theexistence of the solder balls 130, however, a gap 120 a having a heightH is undesirably left under the flip chip 120. It is to be noted that,during the fabrication of the metal dam 111 in the previous step, thethickness T of the metal dam 111 should be smaller than the height H ofthe gap 120 a under the flip chip 120; otherwise, it would obstruct thecleaning of the package body after subsequent flip-chip bonding process.

[0025] Referring further to FIG. 3C, in the next step, a dispensingneedle 140 is used to dispense a predetermined amount of an underfillmaterial, such as resin 141, onto the fillet area 110 a between themetal dam 111 and the flip chip 120. The dispensed resin 141 will thenfill into the gap 120 a under the flip chip 120 through capillaryaction. During the underfill process, thanks to the provision of themetal dam 111, the dispensed resin 141 would be confined within thefillet area 110 a to flow only toward the gap 120 a under the flip chip120 without flashing to other areas on the substrate 110. After theunderfill process is completed, the underfilled resin 141 would includea fillet part 141 a over the fillet area 110 a. Owing to the provisionof the metal dam 111, the fillet part 141 a of the underfilled resin 141would have a fixed width substantially equal to the predefined width Wof the fillet area 110 a.

[0026] It is a characteristic feature of the invention that the metaldam 111 alone can serve three different utilization purposes. First, itcan provide the above-mentioned confining effect to the dispensed resin141 for the defining of a fixed fillet width. Second, since metal istypically much stiffer than organic substance, the metal dam 111 canserve as a mechanical reinforcement to the organic substrate 110,allowing the entire package structure to be more robust to preventpackage warpage. Third, since metal is typically thermally conductive,the metal dam 111 can additionally serve as a heat-dissipation structureto help dissipate the heat produced by the flip chip 120 during activeoperation.

[0027] Referring further to FIG. 3D, in order to help further increasethe efficiency of heat dissipation from the flip chip 120, a heat sink150 having a recessed portion 151 can be additionally mounted over themetal dam 111, with the recessed portion 151 thereof accommodating theflip chip 120. This provision allows the total heat-dissipation surfaceon the package structure to be increased.

[0028] In conclusion, the invention provides a new flip-chip packagingtechnology which is characterized in the use of a metal dam capable ofserving three utilization purposes: (1) providing a specific filletwidth to allow the joint between the flip chip and the substrate to haveoptimal resistance against thermal stress; (2) serving as a mechanicalreinforcement to the substrate to prevent package warpage; and (3)serving as a heat-dissipation structure to help heat dissipation fromthe flip chip. These benefits allow the finished package product to behighly assured in quality and reliability. The invention is thereforemore advantageous to use than the prior art.

[0029] The invention has been described using exemplary preferredembodiments. However, it is to be understood that the scope of theinvention is not limited to the disclosed embodiments. On the contrary,it is intended to cover various modifications and similar arrangements.The scope of the claims, therefore, should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements.

What is claimed is:
 1. A semiconductor package structure, comprising:(a) a substrate; (b) a semiconductor chip mounted over the substratethrough flip-chip technology, with a gap existing between thesemiconductor chip and the substrate; (c) a metal dam formed around thesemiconductor chip over the substrate, the metal dam being dimensionedto a predetermined thickness and separated from the semiconductor chipby a fillet area of a predetermined width; and (d) an underfill layerformed in the gap under the semiconductor chip, the underfill layerhaving a fillet part lying over the fillet area.
 2. The semiconductorpackage structure of claim 1, further comprising: (e) a heat sink havinga recessed portion mounted over the metal dam, with the recessed portionthereof accommodating the semiconductor chip.
 3. The semiconductorpackage structure of claim 1, wherein the predetermined thickness of themetal dam is smaller than the height of the gap between thesemiconductor chip and the substrate.
 4. The semiconductor packagestructure of claim 3, wherein the predetermined thickness of the metaldam is from 5 μm to 70 μm.
 5. The semiconductor package structure ofclaim 1, wherein the predetermined fillet width is from 0.5 mm to 2.5mm.
 6. The semiconductor package structure of claim 1, wherein theunderfill material is resin.
 7. A semiconductor package fabricationprocess, comprising the steps of: (1) preparing a substrate having acenter area predefined as a die-bonding area; (2) forming a metal damaround the die-bonding area over the substrate, the metal dam beingdimensioned to a predetermined thickness and separated from thedie-bonding area by a fillet area of a predetermined fillet width; (3)mounting a semiconductor chip onto the die-bonding area over thesubstrate through flip-chip technology, and in which process a gap isundesirably left between the semiconductor chip and the substrate; and(4) dispensing an underfill material onto the fillet area, the dispensedunderfill material subsequently filling into the gap between thesemiconductor chip and the substrate through capillary action, therebyforming an underfill layer having a fillet part over the fillet area,with the width of the fillet part being substantially equal to thepredetermined width of the fillet area.
 8. The semiconductor packagefabrication process of claim 7, further comprising the step of: (5)mounting a heat sink having a recessed portion over the metal dam, withthe recessed portion thereof accommodating the semiconductor chip. 9.The semiconductor package fabrication process of claim 7, wherein insaid step (2), the predetermined thickness of the metal dam is smallerthan the height of the gap between the semiconductor chip and thesubstrate.
 10. The semiconductor package fabrication process of claim 9,wherein in said step (2), the predetermined thickness of the metal damis from 5 μm to 70 μm.
 11. The semiconductor package fabrication processof claim 7, wherein in said step (2), the predetermined fillet width isfrom 0.5 mm to 2.5 mm.
 12. The semiconductor package fabrication processof claim 7, wherein in said step (4), the underfill material is resin.13. A semiconductor package fabrication process, comprising the stepsof: (1) preparing a substrate having a center area predefined as adie-bonding area; (2) forming a metal dam around the die-bonding areaover the substrate, the metal dam being dimensioned to a predeterminedthickness and separated from the die-bonding area by a fillet area of apredetermined fillet width; (3) mounting a semiconductor chip onto thedie-bonding area over the substrate through flip-chip technology, and inwhich process a gap is undesirably left between the semiconductor chipand the substrate; (4) dispensing an underfill material onto the filletarea; the dispensed underfill material subsequently filling into the gapbetween the semiconductor chip and the substrate through capillaryaction, thereby forming an underfill layer having a fillet part over thefillet area, with the width of the fillet part being substantially equalto the predetermined width of the fillet area; and (5) mounting a heatsink having a recessed portion over the metal dam, with the recessedportion thereof accommodating the semiconductor chip.
 14. Thesemiconductor package fabrication process of claim 13, wherein in saidstep (2), the predetermined thickness of the metal dam is smaller thanthe height of the gap between the semiconductor chip and the substrate.15. The semiconductor package fabrication process of claim 14, whereinin said step (2), the predetermined thickness of the metal dam is from 5μm to 70 μm.
 16. The semiconductor package fabrication process of claim13, wherein in said step (2), the predetermined fillet width is from 0.5mm to 2.5 mm.
 17. The semiconductor package fabrication process of claim13, wherein in said step (4), the underfill material is resin.